Coupled CH4, CO2, and N2O cycling in a subsurface serpentinising system
Coupled CH4, CO2, and N2O cycling in a subsurface serpentinising system
Serpentinising systems are among the most plausible environments for life’s emergence, where reactions between water and ultramafic rocks generate hydrogen, methane, and simple organics that could have fuelled early metabolisms. These reactions create highly alkaline fluids and steep pH–redox gradients that persist today, sustaining diverse microbial processes that regulate greenhouse gas fluxes. Here, we examined subsurface fluids from the Samail Ophiolite (Oman), the world’s largest and best-exposed terrestrial serpentinising system, to characterise greenhouse gas dynamics and their interconnections across contrasting geochemical conditions. CH4 concentrations increased markedly with pH and were highly supersaturated (up to 48,000× atmospheric equilibrium) in reduced, hyperalkaline fluids (pH > 11), indicating strong net production. In contrast, CO2 concentrations decreased with pH, consistent with substantial CO2 consumption and carbonate precipitation under hyperalkaline conditions, whereas CO2 remained elevated in pH-neutral, oxidised fluids. N2O concentrations were low (0.001–1.5 μM) and showed strong net consumption under hyperalkaline, reducing conditions. However, addition of CH4 alongside 15N-nitrite stimulated N2O production — up to 72-fold higher in hyperalkaline fluids, revealing a mechanistic link between CH4 and N2O cycling. Isotopic data (45N2O, 46N2O) further indicated depth- and pH-dependent shifts in dominant N2O pathways. Our findings show that interactions between geological and microbial processes control the balance of greenhouse gas production and consumption in serpentinising systems. These insights illuminate how life and geochemistry interact under extreme conditions, with implications for modern CO2 storage strategies and ancient Earth environments.
Si, Yueyue
da0cbb1d-cec8-426a-b537-4c7d4e2c1ef0
Stocker, Michael
af0c98d3-82b2-486e-b12f-a62e8bc95efc
Shannon, Joanna
403e75fb-9a07-47cc-b43a-405c90e3a38b
Matter, Juerg
abb60c24-b6cb-4d1a-a108-6fc51ee20395
Lam, Phyllis
996aef80-a15d-4827-aed8-1b97b378f6ad
14 March 2026
Si, Yueyue
da0cbb1d-cec8-426a-b537-4c7d4e2c1ef0
Stocker, Michael
af0c98d3-82b2-486e-b12f-a62e8bc95efc
Shannon, Joanna
403e75fb-9a07-47cc-b43a-405c90e3a38b
Matter, Juerg
abb60c24-b6cb-4d1a-a108-6fc51ee20395
Lam, Phyllis
996aef80-a15d-4827-aed8-1b97b378f6ad
Si, Yueyue, Stocker, Michael, Shannon, Joanna, Matter, Juerg and Lam, Phyllis
(2026)
Coupled CH4, CO2, and N2O cycling in a subsurface serpentinising system.
In EGU General Assembly 2026.
(doi:10.5194/egusphere-egu26-19847).
Record type:
Conference or Workshop Item
(Paper)
Abstract
Serpentinising systems are among the most plausible environments for life’s emergence, where reactions between water and ultramafic rocks generate hydrogen, methane, and simple organics that could have fuelled early metabolisms. These reactions create highly alkaline fluids and steep pH–redox gradients that persist today, sustaining diverse microbial processes that regulate greenhouse gas fluxes. Here, we examined subsurface fluids from the Samail Ophiolite (Oman), the world’s largest and best-exposed terrestrial serpentinising system, to characterise greenhouse gas dynamics and their interconnections across contrasting geochemical conditions. CH4 concentrations increased markedly with pH and were highly supersaturated (up to 48,000× atmospheric equilibrium) in reduced, hyperalkaline fluids (pH > 11), indicating strong net production. In contrast, CO2 concentrations decreased with pH, consistent with substantial CO2 consumption and carbonate precipitation under hyperalkaline conditions, whereas CO2 remained elevated in pH-neutral, oxidised fluids. N2O concentrations were low (0.001–1.5 μM) and showed strong net consumption under hyperalkaline, reducing conditions. However, addition of CH4 alongside 15N-nitrite stimulated N2O production — up to 72-fold higher in hyperalkaline fluids, revealing a mechanistic link between CH4 and N2O cycling. Isotopic data (45N2O, 46N2O) further indicated depth- and pH-dependent shifts in dominant N2O pathways. Our findings show that interactions between geological and microbial processes control the balance of greenhouse gas production and consumption in serpentinising systems. These insights illuminate how life and geochemistry interact under extreme conditions, with implications for modern CO2 storage strategies and ancient Earth environments.
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Published date: 14 March 2026
Venue - Dates:
EGU General Assembly, , Vienna, Austria, 2026-05-03 - 2026-05-08
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Local EPrints ID: 510765
URI: http://eprints.soton.ac.uk/id/eprint/510765
PURE UUID: 36da20f3-a100-4a67-aaf6-d7bd65455036
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Date deposited: 21 Apr 2026 16:49
Last modified: 22 Apr 2026 02:08
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Author:
Yueyue Si
Author:
Michael Stocker
Author:
Joanna Shannon
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